Colloidal bismuth subcitrate (CBS) was initially an effective drug in treating H. pylori infection with a three-dimensional anionic framework composing of bismuth dimeric units,1 and diverse structures are also observed with different cations.2 Therefore, CBS is found to be a flexible, porous and low cytotoxic material which could be a potential metal-organic framework (MOF) for drug delivery.

In this presentation, we cocrystallized CBS with small molecule spermidine. Crystallography data show a bismuth MOF porous structure with the channel size of 17.9×14.6 Å, which is the most extensive channel found within CBS-MOF. This nontoxic and thermally stable MOF also exhibits efficient loading of commercial drugs like metformin, isoniazid, entecavir, remdesivir and cisplatin. The loading ability was characterized by HPLC, electron diffraction X-ray- scanning electron microscopy (EDX-SEM) and X-ray photoelectron spectroscopy (XPS). Meanwhile, co-crystallization also revealed a bismuth cluster which shares similar clustering pattern of bismuth citrates from the previous literature. Thus, it shows the high tendency of bismuth citrate forming clusters by aggregation. The two crystal structures therefore unveil the possibility of building new polymeric bismuth citrate architectures for applications by co-crystallizing with anionic guest molecules.

We thank the Research Grants Council (RGC) (R7070-18, 17308921, 2122-7S04) and ITF of Hong Kong, the University of Hong Kong (URC and Norman & Celia Yip Foundation) for financial support.

1. Li W, Jin, L, Zhu N, Sun, H. et al J. Am. Chem. Soc., 2003, 125, 12408 – 12409. 
2. Yang, N.; An, Y.; Sun, H. et al Sci. China Chem., 2010, 53, 2152 – 2158.